Polystyrene resins have been attracting people's attention since they were discovered due to their advantages such as stable physical and chemical properties, easy regeneration operation and long service life. Cation-anion exchange resin prepared by the modification of polystyrene polymer particles is a kind of resin which is yielded the greatest in the world at present, and has been widely applied in fields such as water softening, purification of drugs and foods, material recycling, reclamation of pollutants and catalysis, with great influence on the development of the electric power industry, the chemical engineering, the pharmaceutical industry and the military industry.
At present, polystyrene is usually prepared by suspension polymerization. Generally, the oil phase containing styrene and divinylbenzene as main monomers is added to an aqueous solution dissolved with dispersants and salts (the dispersed phase) for suspension polymerization in the presence of initiators. The composition of the dispersants and the control of stirring have great influence on the particle size of polymers and the particle size distribution. At present, as industrial dispersants, synthetic dispersants such as gelatin, polyvinyl alcohol, polyvinylpyrrolidone, hydroxymethyl cellulose, hydroxyethyl cellulose, sodium dodecyl benzene sulfonate and sodium lignin sulfonate are used. Such dispersants are short in service life and cannot be reused. As a result, a large amount of wastewater containing a high content of dispersants and a high content of salts is produced. Furthermore, it is difficult to biodegrade such dispersants and this causes great harm to the environment. Generally, the particle size of polymers can be distributed normally between 0.3 mm and 0.9 mm, by adjusting the composition of dispersants in the dispersed phase and the concentration thereof, accompanied by the control of the stirring speed. However, during the treatment of large-flow water, resin particles of a large particle size facilitate the increase of flow. Unfortunately, those traditional dispersants are inappropriate for the preparation of resins of a uniform and large particle size (>1 mm). At present, there has been no any report about methods for synthesis of uniform- and large-particle-size particles. For example, by the method disclosed in the authorized patent ZL201210486496.9, entitled “PREPARATION METHOD OF CROSSLINKED POLYSTYRENE RESIN MICROSPHERES WITH NARROW PARTICLE SIZE DISTRIBUTION”, relatively uniform polystyrene particles can be prepared. However, their particle size is adjustable between 53 μm and 350 μm. Meanwhile, during the polymerization, the dispersed phase in the traditional synthesis methods usually contains gelatin and a high concentration of inorganic salts such as sodium chloride, and consequently, the dispersed phase at the end of synthesis cannot be recycled. The preparation process is not green and environmentally friendly. The development of this industry is highly restricted.